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Volume 21 Issue 12
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Original Articles
New Symmetries for a Model of Fast Diffusion
QIN Mao-Chang, XU Xue-Jun, MEI Feng-Xiang
Chin. Phys. Lett. 2004, 21 (12): 2323-2326 .  
Abstract   PDF(pc) (182KB) ( 525 )
The new symmetries for a mathematical model of fast diffusion are determined. A new system method is given to search for new symmetries of differential equations written in a conserved form, several new symmetry generators and exact solutions are presented.
Rescaling Symmetry Flow of the Kadomtsev--Petviashvili Hierarchy
WANG Ning
Chin. Phys. Lett. 2004, 21 (12): 2327-2329 .  
Abstract   PDF(pc) (183KB) ( 546 )
We present a new symmetry flow of the Kadomtsev--Petviashvili (KP) hierarchy, which origins from the rescaling of whole "multi-time" valuables. This flow describes the deformation of solutions of the KP hierarchy with respect to a noncommutative parameter. It is shown that the introduced rescaling symmetry flow does not commute with the ordinary evolution flows of the KP hierarchy, but commutes with the evolution flows with respect to slow-variables.
Generalized Supersymmetric Perturbation Theory
B.Gö, nül
Chin. Phys. Lett. 2004, 21 (12): 2330-2333 .  
Abstract   PDF(pc) (183KB) ( 409 )
Using the basic ingredient of supersymmetry, a simple alternative approach is developed to perturbation theory in one-dimensional non-relativistic quantum mechanics. The formulae for the energy shifts and wavefunctions do not involve tedious calculations which appear in the available perturbation theories. The model applicable in the same form to both the ground state and excited bound states, unlike the recently introduced supersymmetric perturbation technique which, together with other approaches based on logarithmic perturbation theory, are involved within the more general framework of the present formalism.
Analytical Solution and Production of Coherent State of the Generalized Dissipative Two-Mode Optical System
HOU Bang-Pin, WANG Shun-Jin, YU Wan-Lun, SUN Wei-Li, WANG Gang
Chin. Phys. Lett. 2004, 21 (12): 2334-2337 .  
Abstract   PDF(pc) (300KB) ( 860 )
We obtain the analytical solution to the master equation in the photon number representation by using algebraic dynamical method in the nonautonomous case. Based on the solution we find that a two-mode coherent sate can be produced within dissipative background, and the averaged photon number for each mode is related to the damping constant, external field amplitude and coupling constant between two modes.
Rotationally Invariant Proof of Bell’s Theorem Without Inequalities for 4k-Dimensional (k=1,2,...) Systems
LIANG Lin-Mei, LI Cheng-Zu
Chin. Phys. Lett. 2004, 21 (12): 2338-2339 .  
Abstract   PDF(pc) (172KB) ( 456 )
We present rotationally invariant proof of Bell’s theorem without inequalities for spin-2N+1/2 system (N= 2k-1, k=1,2,3,4 ...) with only two particles, which is a generalization of Cabello's study [Phys. Rev. A 67 (2003) 032107].

Cai--Li Communication Protocol in Noisy Quantum Channel
Lü Hua, YAN Xu-Dong, ZHANG Xian-Zhou
Chin. Phys. Lett. 2004, 21 (12): 2340-2342 .  
Abstract   PDF(pc) (231KB) ( 687 )
Since the original Cai--Li protocol [Chin. Phys. Lett. 21(2004)601] can be used only in an ideal quantum communication, we present the modified Cai--Li protocol that can be used in the a noisy quantum channel by using Calderbank--Shor--Steane (CSS) codes to correct errors. We also give a tight bound on the connection between information Eve eavesdropped with a measurement attack in line B → A and detection probability, which shows that the Cai--Li protocol can be used as a quasisecure direct quantum communication.
Demonstration of Quantum Entanglement Control Using Nuclear Magnetic Resonance
XIE Jing-Yi, ZHANG Jing-Fu, DENG Zhi-Wei, LU Zhi-Heng
Chin. Phys. Lett. 2004, 21 (12): 2343-2346 .  
Abstract   PDF(pc) (378KB) ( 410 )
With the two forms of the quantum entanglement control, the quantum entanglement swapping and preservation are demonstrated in a three-qubit nuclear magnetic resonance quantum computer. The pseudopure state is prepared to represent the quantum entangled states through macroscopic signals. Entanglement swapping is directly realized by a swap operation. By controlling the interactions between the system and its environment, we can preserve an initial entangled state for a longer time. The experimental results are in agreement with the experiment.
Explicit Analysis of Creating Maximally Entangled State in the Mott Insulator State
LI Min-Si, TIAN Li-Jun, ZHANG Hong-Biao
Chin. Phys. Lett. 2004, 21 (12): 2347-2350 .  
Abstract   PDF(pc) (219KB) ( 478 )
We clarify the essence of the method proposed by You (Phys. Rev. Lett. 90(2004)030402) to create the maximally entangled atomic N-GHZ state in the Mott insulator state. Based on the time-independent perturbation theory, we find that the validity of the method can be summarized as that the Hamiltonian governing the evolution is approximately equivalent to the type aJ2x+bJx, which is the well known form used to create the maximally entangled state.
Effects of the Scattering Length on the Yrast Spectrum for a Two-Component Bose--Einstein Condensates
YU Yang, LUO Bin, LIU Kun, ZHOU Xiao-Ji, CHEN Xu-Zong
Chin. Phys. Lett. 2004, 21 (12): 2351-2354 .  
Abstract   PDF(pc) (263KB) ( 431 )
We study the energy eigenvalue and the yrast states for a harmonically two-component weak-interacting Bose--Einstein condensate (BEC) when the intra-species and interspecies scattering length are different. The energy shift for different energy eigenvalues related to intra- and interspecies scattering lengths is calculated with the perturbation method. The actual yrast spectrum is more complicated than that when intra-species and interspecies scattering length are equal. The degenerated features disappear and so do the perfect symmetric features.

Phase Diagram and Phase Separation of a Trapped Interacting Bose--Fermi Gas Mixture
MA Yong-Li
Chin. Phys. Lett. 2004, 21 (12): 2355-2358 .  
Abstract   PDF(pc) (254KB) ( 443 )
In six different regimes for a spatial phase diagram of a trapped interacting Bose--Fermi gas mixture at low temperatures, we present the conditions for the spatial demixing and separation of bosons and fermions. Starting from a semiclassically thermodynamic model for the local density functional of thermal bosons and fermions, the explicit analytical expressions for the fugacities of bosons and fermions are derived in different regimes by means of a first-order perturbation method in a local-density approximation. The critical values of the fermion--boson interaction strength as a function of the fractional composition of fermions have a general feature: increase, extreme and decrease with increasing the fermionic composition slightly above Bose--Einstein critical temperature.
Non-Static Plane Symmetric Zeldovich Fluid Model In Scale Invariant Theory
B. Mishra
Chin. Phys. Lett. 2004, 21 (12): 2359-2361 .  
Abstract   PDF(pc) (173KB) ( 557 )
The perfect fluid distribution in scale invariant theory of gravitation is studied, when the spacetime is described by non-static plane symmetric metric with a time-dependent gauge function. The Zeldovich model of the universe is constructed and some physical properties of the model are discussed.
Vacuum Fluctuations and Motion of a Charged Test Particle in a Cylindrical Spacetime
CHEN Jun, YU Hong-Wei
Chin. Phys. Lett. 2004, 21 (12): 2362-2364 .  
Abstract   PDF(pc) (178KB) ( 415 )
The effects of quantum electromagnetic fluctuations upon the motion of a test charged particle are examined in a cylindrical spacetime in which one spatial is compactified. The mean squared fluctuations in the velocity and position of the test particle are calculated. It is found that the random motion of the test particle will be anisotropic. The possible consequences for theories with extra compactified spatial dimensions are discussed.

Additive Temporal Coloured Noise Induced Eckhaus Instability in Complex Ginzburg--Landau Equation System
WANG Xin, TIAN Xu, WANG Hong-Li, OUYANG Qi, , LI Hao
Chin. Phys. Lett. 2004, 21 (12): 2365-2368 .  
Abstract   PDF(pc) (405KB) ( 510 )
The effect of additive coloured noises, which are correlated in time, on one-dimensional travelling waves in the complex Ginzburg--Landau equation is studied by numerical simulations. We found that a small coloured noise with temporal correlation could considerably influence the stability of one-dimensional wave trains. There exists an optimal temporal correlation of noise where travelling waves are the most vulnerable. To elucidate the phenomena, we statistically calculated the convective velocities Vg of the wave packets, and found that the coloured noise with an appropriate temporal correlation can decrease Vg, making the system convectively more unstable.
Travelling Wave Solutions of Triple Sine--Gordon Equation
LIU Cheng-Shi
Chin. Phys. Lett. 2004, 21 (12): 2369-2371 .  
Abstract   PDF(pc) (168KB) ( 1177 )
Using a complete discrimination system for polynomials and elementary integral method, we obtain the travelling solutions for triple sine--Gordon equation. This method can be applied to similar problems and has general meaning
Design of Grazing-Incidence Broad-Band Multilayers for Hard X-Ray Reflectors
ZHANG Zhong, WANG Zhan-Shan, WANG Feng-Li, QIN Shu-Ji, CHEN Ling-Yan
Chin. Phys. Lett. 2004, 21 (12): 2372-2375 .  
Abstract   PDF(pc) (421KB) ( 447 )
A new method of designing x-ray supermirrors with broad angular or energy response for use as coatings in x-ray optics is presented. The design is based on an analytical method with oversimplified analytical and semi-empirical formulae, and an extensive numerical method is used in the optimization design. A better initial multilayer is obtained with the former method and optimized with the latter method. In the optimization, a good design is achieved with much less computing time. In addition, the saturation effect due to the interfacial roughness in multilayer also emerges in the design of x-ray supermirrors with definite performances. The reflectivity of C/W x-ray supermirrors as a function of photon energy at the fixed grazing incident angle 0.5°is presented.
Neutrino Mean Free Path in Strange Matter at High Temperatures
MA Zhong-Xiang, ZHAO Yong-Heng
Chin. Phys. Lett. 2004, 21 (12): 2376-2379 .  
Abstract   PDF(pc) (294KB) ( 682 )
We investigate the condition that the neutrino energies Ev can be considered to be small enough to be neglected in the energy momentum conservation equation in the reactions d+ve → u+e- and u+e- → d+ve. It can be simply expressed as Ev < 4αcμe/π, where αc is the strong coupling constant and μe is the electron chemical potential. Then for Ev < 4αcμe/π, we generalize the mean free path for nondegenerate neutrinos given by Iwamoto and obtain a formula that is valid for both nondegenerate and degenerate neutrinos. We also model the mean free path for both nondegenerate and degenerate neutrinos with energies Ev < 4αcμe/π.

Prospects of Bc Mesons at the Compact Muon Solenoid
ZHANG Shao-He, A. A.Belkov, S.Shulga, CHEN Guo-Ming
Chin. Phys. Lett. 2004, 21 (12): 2380-2383 .  
Abstract   PDF(pc) (351KB) ( 602 )
The results of two Monte Carlo generators for production of Bc mesons in pp collisions are compared at the large hadron collider energy √s=14 TeV. In the study, the produced Bc mesons were forced to decay into the final states Bslv, Bsπ, J/ψlv, and J/ψπ. We have estimated that about 104 decays of Bc are expected to be recorded during the first year of the CMS running with a lepton trigger. Many Bc studies can be carried out by using these events with a statistical error at the level of 10-2.
Activation Characteristics of Fuel Breeding Blanket Module in Fusion Driven Subcritical System
HUANG Qun-Ying, LI Jian-Gang, CHEN Yi-Xue
Chin. Phys. Lett. 2004, 21 (12): 2384-2387 .  
Abstract   PDF(pc) (532KB) ( 455 )
Shortage of energy resources and production of long-lived radioactivity wastes from fission reactors are among the main problems which will be faced in the world in the near future. The conceptual design of a fusion driven subcritical system (FDS) is underway in Institute of Plasma Physics, Chinese Academy of Sciences. There are alternative designs for multi-functional blanket modules of the FDS, such as fuel breeding blanket module (FBB) to produce fuels for fission reactors, tritium breeding blanket module to produce the fuel, i.e. tritium, for fusion reactor and waste transmutation blanket module to try to permanently dispose of long-lived radioactivity wastes from fission reactors, etc. Activation of the fuel breeding blanket of the fusion driven subcritical system (FDS-FBB) by D-T fusion neutrons from the plasma and fission neutrons from the hybrid blanket are calculated and analysed under the neutron wall loading 0.5MW/m2 and neutron fluence 15MW.yr/m2. The neutron spectrum is calculated with the worldwide-used transport code MCNP/4C and activation calculations are carried out with the well known European inventory code FISPACT/99 with the latest released IAEA Fusion Evaluated Nuclear Data Library FENDL-2.0 and the ENDF/B-V uranium evaluated data. Induced radioactivities, dose rates and afterheats, etc, for different components of the FDS-FBB are compared and analysed.
Single-Walled Carbon Nanotubes Acting as Controllable Transport Channels
HUANG Bo-Da, XIA Yue-Yuan, ZHAO Ming-Wen, LI Feng, LIU Xiang-Dong, JI Yan-Ju, SONG Chen, TAN Zhen-Yu, LIU Hui
Chin. Phys. Lett. 2004, 21 (12): 2388-2391 .  
Abstract   PDF(pc) (454KB) ( 691 )
The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged single-walled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.

Bichromatic Coherent Population Trapping Under Hanle Configuration
WANG Yi, , HU Zheng-Feng, XU Xin-Ping, ZHANG Peng-Fei, ZHANG Hai-Chao, LIU Hua, ZHAN Ming-Sheng, WANG Yu-Zhu,
Chin. Phys. Lett. 2004, 21 (12): 2392-2394 .  
Abstract   PDF(pc) (310KB) ( 421 )
We report the observation of bichromatic coherent population trapping under the transition 87RbFg =1 → Fe = 0 with two linearly polarized laser beams by means of a Hanle effect configuration. The mechanism behind this effect is identified, and numerical solutions for the pump rates equations are presented.

Calculation of Elastic Scattering Properties in an Ultra-Cold 85Rb--85Rb Vapour
M.Kemal Ö, ztürk, Süleyman Ö, zcelk
Chin. Phys. Lett. 2004, 21 (12): 2395-2398 .  
Abstract   PDF(pc) (427KB) ( 374 )
We report the calculation of the same-species elastic scattering properties for the ultracold rubidium--rubidium (85Rb--85Rb) system and the results are compared with other theoretical and experimental results in detail. We present an improved potential for triplet ground states of the Rb2 molecule, and calculate the scattering lengths at and the effective range r3 using WKB and Numerov methods for two rubidium-85 collisions in the triplet state. Also, we investigate the convergence of these scattering properties, i.e. the dependence on core radius and K0 parameter using quantum defect theory and the analytic calculations of scattering length obtained by Szmytkowski. In addition, we present evaporative cooling and other results that include phase shift and cross section at zero energy limit.
One- and Two-Dimensional Arrays of Double-Well Optical Traps for Cold Atoms or Molecules
JI Xian-Ming, YIN Jian-Ping
Chin. Phys. Lett. 2004, 21 (12): 2399-2402 .  
Abstract   PDF(pc) (293KB) ( 375 )
We propose a novel scheme to form one- and two-dimensional arrays of double-well optical dipole traps for cold atoms (or molecules) by using an optical system composed of a binary π-phase grating and a lens illuminated by a plane light wave, and study the relationship between the maximum intensity Imax of each optical well (or the maximum trapping potential Umax for 85Rb atoms) and the relative aperture β(= a/f) of the lens. We also calculate the intensity gradients of each optical well and their curvatures, and estimate the spontaneous photon-scattering rate of trapped atom in each well, including Rayleigh and Raman scattering rates. Our study shows that the proposed 1D and 2D arrays of double-well traps can be used to prepare 1D and 2D novel optical lattices with cold atoms (or molecules), or form an all-optically integrated atom optical chip, or even to realize an array of all-optical double-well atomic (or molecular) Bose--Einstein condensates by optical-potential evaporative cooling, and so on.
Effect of Polarization in (e,2e) Ionization of Argon
HU Xiao-Ying, ZHOU Ya-Jun
Chin. Phys. Lett. 2004, 21 (12): 2403-2405 .  
Abstract   PDF(pc) (277KB) ( 374 )
The triple differential cross section of the Ar 2p orbital in a highly asymmetric geometry is calculated by using a modified distorted wave Born approximation method. A short-range polarization potential via density-functional theory is included in our calculations. It is shown that polarization potential is particularly important for calculations of the triple differential cross section.
Positronium Formation in e+--K Collision at Low Energies
NAN Guang-Jun, ZHOU Ya-Jun, KE You-Qi
Chin. Phys. Lett. 2004, 21 (12): 2406-2409 .  
Abstract   PDF(pc) (379KB) ( 357 )
Positronium (Ps) formation cross section for positron scattering on potassium is calculated at low impact energies (0.2--15.0eV). The present calculation uses an optical-model method with an equivalent local polarization potential. The results for the Ps (n=1) and Ps (n=2) formation cross sections are calculated and compared with the experimental measurements and other theoretical results.
Time-Dependent Local Density Approximation Calculations for Absorption Spectra of Small Carbon Clusters
BAI Yu-Lin, CHENG Xiao-Hong, CHENG Yan, CHEN Xiang-Rong, YANG Xiang-Dong,
Chin. Phys. Lett. 2004, 21 (12): 2410-2413 .  
Abstract   PDF(pc) (467KB) ( 481 )
Absorption spectra for Cn clusters (n=2--8) are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (TDLDA). We compare the calculated spectra with those computed using a simple local density approximation approach. It is readily observed that the TDLDA spectra display a significant blue shift with respect to the Kohn--Sham eigenvalue spectra. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. We also obtain a significant threshold absorption, which can distinguish different ground states of the carbon clusters.
Effect of Cluster Coulomb Fields on Electron Acceleration in Laser--Cluster Interaction
CANG Yu, DONG Quan-Li, WU Hui-Chun, SHENG Zheng-Ming, YU Wei, ZHANG Jie
Chin. Phys. Lett. 2004, 21 (12): 2414-2417 .  
Abstract   PDF(pc) (508KB) ( 514 )
Single particle simulations are used to investigate electron acceleration in the laser--cluster interaction, taking into account the Coulomb fields around individual clusters. These Coulomb fields are induced from the cluster cores with positive charge when electrons escape from the cluster cores through ponderomotive push from the laser field. These Coulomb fields enable some stripped electrons to be stochastically in phases with the laser fields so that they can gain net energy from the laser efficiently. In this heating mechanism, circularly polarized lasers, larger cluster size and higher cluster densities make the acceleration more efficient.
Dynamic Behaviour of Self-Diffraction in Bacteriorhodopsin Film
GUO Zong-Xia, CHEN Gui-Ying, ZHANG Chun-Ping, TIAN Jian-Guo, Q. Wang Song, SHEN Bin, FU Guang-Hua
Chin. Phys. Lett. 2004, 21 (12): 2418-2421 .  
Abstract   PDF(pc) (462KB) ( 418 )
We investigate the dependences of the diffraction efficiency of the first order self-diffracted beam in bacteriorhodopsin (bR) films on the illumination time, the intensity and wavelength of the incident light. When the blue light ( λ = 488nm) and low intensity red light ( λ = 632.8nm) are incident on the bR film respectively, the diffraction efficiencies increase from zero to a stable value with the illumination time. When the green light ( λ = 533nm) and high-intensity red light illuminate the bR film respectively, the diffraction efficiencies increase from zero to the maximum and then decrease to a stable value with the illumination time. Rise and decay times are dependent on the intensity and wavelength of the incident light. The maximal diffraction efficiency of the red light is twice as high as that of the green light. The highest diffraction efficiency of 5.4% is obtained at 633 nm. The diffraction efficiency change with the time for the green light is larger than that for the blue and red light.
Three-Rod Resonator for Krypton Lamp Pumped 1.8 kW Continuous-Wave Nd:YAG Laser
LI Qiang, FANG Ming-Xing, WANG Zhi-Yong, YU Zhen-Sheng, LEI Hong, GUO Jiang, LI Gang, ZUO Tie-Chuan
Chin. Phys. Lett. 2004, 21 (12): 2422-2425 .  
Abstract   PDF(pc) (415KB) ( 483 )
A three-rod series resonator cw Nd:YAG laser suitable for the industrial applications is presented. The symmetrical resonator laser has been developed and is rated at 1820-W output power with beam parameter product 24mm.mrad. By utilizing the symmetrical resonator design, the characteristic of beam with multi-rod is not obviously decreased compared with that of a single one. The system total electro-optics efficiency of lamp pumped YAG crystal is as high as 4.0%. The main factors, which affect output power and beam quality of high power solid-state laser module, are theoretically analysed.
Experimental Investigation of High Power Erbium--Ytterbium Co-doped Double Clad Fibre Laser
LI Li-Jun, FENG Xin-Huan, LIU Yan-Ge, LI Yao, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2004, 21 (12): 2426-2428 .  
Abstract   PDF(pc) (412KB) ( 697 )
All-fibre high power erbium--ytterbium co-doped double clad fibre lasers are proposed and demonstrated. By using different back-cavity mirrors, the different double clad fibre lasers are constructed. It is experimentally found that the output behaviour of laser can be controlled by a back-cavity mirror. The lower the reflectivity of the back-cavity mirror, the higher the output power and the high the slop efficiency. The maximum output power is about 1.6\,W and the slop efficiency is 27.6%.
Compensation for Self-Focusing of Picosecond Pulses in Nd:Glass by Using Cascaded Quadratic Nonlinearity
CHEN Hao, WEN Shuang-Chun, ZHU He-Yuan, QIAN Lie-Jia
Chin. Phys. Lett. 2004, 21 (12): 2429-2432 .  
Abstract   PDF(pc) (0KB) ( 341 )
One of the obstacles in obtaining high power/energy laser sources is self-focusing, which stems from the nonlinear phase shift (B-integral) accumulated during beam propagation in Kerr media. Phase-mismatched second-harmonic generation may impose a nonlinear phase shift on the fundamental with controllable sign and magnitude, which can be used to compensate for self-focusing with a single-pass configuration. We have demonstrated such a possibility for picosecond pulses theoretically and experimentally, and both configurations of pre- and post-compensation by a β-barium borate crystal have been studied in detail. Cascaded second-order nonlinearity-based compensation for self-focusing may provide an auxiliary means to the conventional B-integral control techniques.
Hyperpolarizabilities of Chiral Molecules Based on Three-Coupled-Oscillator Model
WANG Xiao-Ou, LI Jun-Qing, LI Chun-Fei
Chin. Phys. Lett. 2004, 21 (12): 2433-3436 .  
Abstract   PDF(pc) (277KB) ( 377 )
A chiral molecular model of three coupled oscillators is established. A set of coupling equations and hyperpolarizabilities for the chiral molecules with the tripod structure are presented. The expression of second-order nonlinear susceptibility is derived for an isotropic molecular system. The calculated hyperpolarizabilities of NPAN and NPP chiral molecules are consistent with the experimental results and the applicability of this model is validated.
Three-Wave Resonant Interaction in Optical Fibres on a Continuous-Wave Background
CUI Wei-Na, HUANG Guo-Xiang
Chin. Phys. Lett. 2004, 21 (12): 2437-2440 .  
Abstract   PDF(pc) (436KB) ( 391 )
We predict that a three-wave resonant interaction (TWRI) for the excitations created from a continuous-wave background is possible in nonlinear optical fibres with a centro-symmetry. We show that in normal dispersion regime and near the zero-dispersion point of a single-mode optical fibre, the phase-matching condition for the TWRI can be satisfied by suitably choosing the wavevectors and frequencies of the exciting waves. The nonlinear envelope equations for the TWRI are derived by using a method of multiple-scales, and their explicit solutions for sum- and difference-frequency mixing are provided and discussed.
Generalized Theory of One-Dimensional Steady-State Optical Spatial Solitons
WANG Hong-Cheng, WANG Xiao-Sheng, SHE Wei-Long
Chin. Phys. Lett. 2004, 21 (12): 2441-2444 .  
Abstract   PDF(pc) (347KB) ( 346 )
We present a generalized soliton theory based on the one-dimensional generalized nonlinear Schrödinger equation, from which one can easily obtain the bright, dark, and grey soliton waveforms, and their existence curves. We show that the forming conditions of spatial solitons are directly dependent on the relationship between the index perturbation and the intensity, no matter whether the index perturbation is positive or negative. Some relevant examples are presented when the solitons are supported by the photoisomerization nonlinearity.
Polarized Emission of an Eu3+ Doped Azo-Polymer Waveguide
WANG Dong, ZHANG Jiang-Ying, MING Hai, YAN Qing, ZHANG Qi-Jin, WANG Pei, YANG Jun, ZHENG Zhi-Qiang
Chin. Phys. Lett. 2004, 21 (12): 2445-2447 .  
Abstract   PDF(pc) (311KB) ( 423 )
We investigate the polarized emission behaviour of an Eu3+ doped azo-polymer waveguide. Affected by the azobenzene groups in the photoinduced orientation process by the 532nm linearly polarized laser, the ligands were realigned orderly perpendicular to the direction of the orientation direction. This leads to the polarized absorption and emission of the waveguide in the orientation direction. By an m-line apparatus based on the prism coupling technique, two guided propagation modes were observed in the waveguide, and the refractive index at 650nm in TE polarizations is 1.7505.
High-Flexible Single-Polarization Single-Mode Photonic-Crystal Fibre
LOU Shu-Qin, YAN Feng-Ping, REN Guo-Bin, JIAN Shui-Sheng
Chin. Phys. Lett. 2004, 21 (12): 2448-2451 .  
Abstract   PDF(pc) (373KB) ( 522 )
We propose a new type of high flexible single-polarization single-mode (SPSM) photonic crystal fibre (PCF). Numerical analysis indicates that the SPSM PCF proposed guides only one polarization mode over a wavelength band broader than the conventional SPSM fibres. The position and the bandwidth of the single polarization mode region depend flexibly on the structure parameters such as the hole diameters d1 and d2 and the hole pitch Λ of the SPSM PCFs. A 200-nm SPSM region can be obtained for the SPSM PCF with Λ=2.55μm, d1/Λ=0.3 and d2/Λ=0.833 and the modal birefringence at the wavelength 1.31μm can reach 1.8×10-3.
Enhancement of Gain in L-Band Bismuth-Based Erbium-Doped Fibre Amplifier Using an Un-pumped EDF and Midway Isolator
W. Y. Chong, S. W. Harun, H. Ahmad
Chin. Phys. Lett. 2004, 21 (12): 2452-2453 .  
Abstract   PDF(pc) (319KB) ( 607 )
A hybrid L-band erbium-doped fibre amplifier (EDFA) with enhanced gain characteristic is demonstrated without a significant noise figure penalty. It uses a backward C-band amplified stimulated emission from both the ends of a bismuth-based EDFA system to pump an unpumped erbium-doped fibre (EDF) for gain enhancing. The maximum gain enhancement of 4.0dB is obtained at wavelength 1604nm with EDF length of 20m. The gain spectrum is reasonably flat in this amplifier compared with the amplifier without an EDF. The gain varies from 27.4dB to 30.2dB at wavelength region 1564--1608nm with incorporation of 20m EDF. Noise figure also varies from 6.0 to 7.7dB at this wavelength region.

Using Digital Imaging to Characterize Threshold Dynamic Parameters in Porous Media Based on Lattice Boltzmann Method
XU You-Sheng, , LIU Yang, HUANG Guo-Xiang
Chin. Phys. Lett. 2004, 21 (12): 2454-2458 .  
Abstract   PDF(pc) (385KB) ( 527 )
Digital images (DI) and lattice Boltzmann method (LBM) are used to characterize the threshold dynamic parameters of porous media. Two-dimensional representations of the porous structure are reconstructed from segmentation of digital images obtained from a series of tiny samples. The threshold pressure gradients and threshold Péclet numbers are researched on seven test samples by using LBM. Numerical results are in agreement with that obtained by integrating Darcy’s law. The results also indicate that fluids can flow through porous media only if the fluid force is large enough to overcome threshold pressure gradient in porous media. One synthetic case is used to further illustrate the applicability of the proposed technique. In addition, the dynamical rules in our model are local, therefore it can be run on parallel computers with well computational efficiency.
Density Modulation Experiments on HT-7 Tokamak
K. Tanaka, GAO Xiang, JIE Yin-Xian, R. Sakamoto, K. Toi
Chin. Phys. Lett. 2004, 21 (12): 2458-2460 .  
Abstract   PDF(pc) (475KB) ( 764 )
Density modulation experiments are successfully conducted on HT-7 ohmic discharge to investigate particle transport coefficients: diffusion coefficients D and convection velocity V. The particle transport is studied at low (1.5×1019m-3) and high (3×1019 m-3) density regimes. The clear differences are observed that D is 0.42m2/s and 0.17m2/s, V is 4.7m/s (outward) and 1.6 m/s (inward) for low and high density plasmas respectively, where spatially constant D and V(r) = (r/a)V0 were assumed for the analysis.


Nonlinear-Ion-Acoustic-Wave Instability, Threshold, Half Width of Trapped Region and Transition Region
XIAO Zuo, WANG Wen-Qing, HAO Yong-Qiang
Chin. Phys. Lett. 2004, 21 (12): 2461-2464 .  
Abstract   PDF(pc) (413KB) ( 493 )
Nonlinear Landau damping of ion acoustic wave (IAW) is one of the most important phenomena in the ionosphere and in space and laboratory plasma as well. The instability growth rate of the IAW with electron drift, the amplitude threshold for exciting the nonlinear effects, the half widths of the trapped region with the trapped electrons are studied experimentally. Under the experimental conditions, it is shown that there is a frequency range of 140--160 kHz, within which the growth rate has the largest value of about 6×104--1.5×105 s-1. We obtain the transitional region width caused by collisions theoretically and experimentally, for the first time to our knowledge. The experimental results are in good agreement with the theoretical prediction.
Laser Micro-Hole Drilling of Soda-Lime Glass with Femtosecond Pulses
AN Ran, LI Yan, DOU Yan-Ping, FANG Ying, YANG Hong, GONG Qi-Huang
Chin. Phys. Lett. 2004, 21 (12): 2465-2469 .  
Abstract   PDF(pc) (248KB) ( 1133 )
Using tightly focused femtosecond laser pulses, we have drilled micro-holes from the front and rear surface of soda-lime glass in ambient air. The machined holes have small aspect ratio or irregular inner walls. When the drilling is conducted from the rear surface in contact with distilled water, a good quality micro-hole with a high aspect ratio can be obtained. The corresponding formation mechanisms are investigated.
Observation of Radial Propagation of Electrostatic Fluctuations in Edge Plasma of the Sino United Spherical Tokamak
ZHANG Guo-Ping, HE Ye-Xi, WANG Wen-Hao, GAO Zhe, ZENG Li, XIE Li-Feng, FENG Chun-Hua
Chin. Phys. Lett. 2004, 21 (12): 2469-2471 .  
Abstract   PDF(pc) (428KB) ( 539 )
Radial propagation of electrostatic fluctuations in the edge plasma of Sino-United Spherical Tokamak (SUNIST) has been measured using Langmuir probes. The propagation characteristics of the floating potential fluctuations are analysed by the two-point correlation technique. The results show radially outward propagation of the turbulent fluctuations at all measured radial positions. The power-average wavenumber profile is approximately constant in plasma edge region and suddenly increases to the limiter. These results are in good agreement with the model predictions proposed by Mattor which suggests that the drift wave propagation may be a source of edge turbulence.
Radiation Energy Loss from Laser-Heated Shenguang-II Hohlraums
CHANG Tie-Qiang, WANG Guang-Yu, DUAN Qing-Sheng, PEI Wen-Bing, GU Pei-Jun, ZHANG Xing-Hong, DING Yong-Kun, ZHENG Zhi-Jian, YANG Jia-Min, HUANG Tian-Xuan, SUN Ke-Xu
Chin. Phys. Lett. 2004, 21 (12): 2469-2471 .  
Abstract   PDF(pc) (355KB) ( 419 )
The x ray energy loss out of laser-heated hohlraum through laser entrance holes (LEH) is discussed in detail according to a simple theoretical model and is compared with the hohlraum experimental data measured at Shenguang II laser facility. The radiation loss is considered to be composed of two parts, that is, direct contribution from laser spots and re-emitted part from the x ray-heated hohlraum inner wall, and the former accounts for about 20% of the total loss for the Shenguang II hohlraums. Owing to the non-equilibrium characteristics of laser target coupling the direct contribution part is non-equilibrium in spectrum.
First Divertor Operation on the HL-2A Tokamak
YANG Qing-Wei, DING Xuan-Tong, YAN Long-Wen, XUAN Wei-Min, LIU De-Quan, CHEN Liao-Yuan, SONG Xian-Ming, YUAN Bao-Shan, ZHANG Jin-Hua, CAO Zeng, LI Xiao-Dong, MAO Wei-Cheng, ZHOU Cai-Pin, WANG En-Yao, YAN Jian-Cheng, LIU Yong, HL-A team
Chin. Phys. Lett. 2004, 21 (12): 2475-2478 .  
Abstract   PDF(pc) (721KB) ( 608 )
HL-2A device is the first divertor tokamak in China. One of its main subjects is to study the features of the divertor plasma. In the last campaign, the first divertor configuration has been achieved and sustained on the HL-2A tokamak. Here we give a brief description about the HL-2A tokamak, diagnostics arrangements, and the equilibrium analysis results on divertor configuration. The main results of divertor experiments are also presented.
Experimental Investigation on Low Magnetic Field Operation of an Overmoded Slow-Wave High-Power Microwave Generator
ZHANG Jun, ZHONG Hui-Huang, SHU Ting, LUO Ling, WANG Yong
Chin. Phys. Lett. 2004, 21 (12): 2479-2481 .  
Abstract   PDF(pc) (423KB) ( 413 )
The experimental results of an overmoded slow-wave high-power microwave generator operated at low magnetic field are presented. The feasibility of low magnetic field operation is investigated both theoretically and experimentally based on the characteristics of the overmoded slow-wave device. The experiments were carried out at the Spark-2 accelerator. Under the condition of guiding magnetic field strength of 0.55T, diode voltage of 474kV, and beam current of 5.2kA, a microwave was generated with power of 510MW, mode of TM01, and frequency of 9.54GHz. The relative half-width of the frequency spectrum is less than 1%, and the beam-to-microwave efficiency is about 21% in our experiments.

Structural and Dynamic Properties of Amorphous Silicon: Tight-Binding Molecular Dynamics Simulation
HUANG Shi-Ping, WANG Wen-Chuan
Chin. Phys. Lett. 2004, 21 (12): 2482-2485 .  
Abstract   PDF(pc) (503KB) ( 547 )
The tight-binding molecular dynamics simulation has been performed to study structural and dynamical properties of amorphous silicon. It is found that the radial distribution function and static structure factor are in good agreement with the experimental measurements. The bond order parameters Ql are sensitive to the structure change at different quenching rates. For the dynamical properties, we have calculated the vibration and electronic density of states. The simulation results show that the transverse acoustic is in good agreement with the experimental data, and the high frequency transverse optical (TO) peak shifts to the right of the experimental TO peak.

A Mechanism for the Self-Organization of Colloidal Gold Nanoparticles
ZHANG Yong-Jun, HAN Guan-Qi, LI Wei, DAI Min, ZHANG Yu, HUANG Xin-Fan, CHEN Kun-Ji
Chin. Phys. Lett. 2004, 21 (12): 2486-2488 .  
Abstract   PDF(pc) (342KB) ( 515 )
We report a two-stage mechanism of formation of the two-dimensional surperlattices in colloidal gold nanoparticles. The first stage is the formation and growth of holes. When the film is thinner than the "pancake" thickness and because the solvent volatility holes nucleate and grow, the dry solid surface is exposed. The second stage corresponds to the reorganization of the colloids in the impacted areas between several holes, in which the particles gathering along the rims order due to the van der Waals-type attraction between colloids and the confinement by the length of dodecanethiol. Then at a compromised distance and perfect position giving the minimum free energy, ordering occurs in small domains along the boundary of the hole. When the ordered domains become closer because of the hole growth, they rotate at certain angles and the further ordering appears.
Universal Scaling Law for Atomic Diffusion and Viscosity in Liquid Metals
LI Guang-Xu, LIU Chang-Song, ZHU Zhen-Gang
Chin. Phys. Lett. 2004, 21 (12): 2489-2492 .  
Abstract   PDF(pc) (428KB) ( 784 )
The recently proposed scaling law relating the diffusion coefficient and the excess entropy of liquid [Samanta A et al. 2004 Phys. Rev. Lett. 92 145901; Dzugutov M 1996 Nature 381 137], and a quasi-universal relationship between the transport coefficients and excess entropy of dense fluids [Rosenfeld Y 1977 it Phys. Rev. A 15 2545], are tested for diverse liquid metals using molecular dynamics simulations. Interatomic potentials derived from the glue potential and second-moment approximation of tight-binding scheme are used to study liquid metals. Our simulation results give sound support to the above-mentioned universal scaling laws. Following Dzugutov, we have also reached a new universal scaling relationship between the viscosity coefficient and excess entropy. The simulation results suggest that the reduced transport coefficients can be expressed approximately in terms of the corresponding packing density.
Nonmean-Field Model for Ostwald Ripening of Two-Dimensional Islands
LOU Chao-Gang
Chin. Phys. Lett. 2004, 21 (12): 2493-2495 .  
Abstract   PDF(pc) (423KB) ( 482 )
A nonmean-field model for the ripening of two-dimensional islands is presented. In this model, the adatom sea is divided into many small cells that are the polygons of a Voronoi network. The chemical potentials of adatom seas surrounding different islands are different. Strain generated by lattice mismatch is introduced into the model. Computer simulation under periodic boundary conditions is carried out to describe the island ripening in two cases (with and without strain), and demonstrates that small islands may grow faster than large islands, which cannot occur in the mean-field model. The simulated results also show that including strain will slow down the evolution of average island size, and an explanation for this is given.
Role of Interactions in Electronic Structure of a Two-Electron Quantum Dot Molecule
DONG Qing-Rui, XU Ying-Qiang, ZHANG Shi-Yong, NIU Zhi-Chuan
Chin. Phys. Lett. 2004, 21 (12): 2496-2499 .  
Abstract   PDF(pc) (311KB) ( 722 )
We have studied a two-electron quantum dot molecule in a magnetic field. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate two lowest energy levels of the two-electron quantum dot molecule in a magnetic field. Our results show that the electron interactions are significant, as they can change the total spin of the two-electron ground state of the system by adjusting the magnetic field between S=0 and S=1. The energy difference ΔE between the lowest S=0 and S=1 states is shown as a function of the axial magnetic field. We found that the energy difference between the lowest S=0 and S=1 states in the strong-B S=0 state varies linearly. Our results provide a possible realization for a qubit to be fabricated by current growth techniques.
Effects of Crossed Electric and Magnetic Fields on Shallow Donor Impurity Binding Energy in a Parabolic Quantum Well
E. Kasapoglu, H. Sari, I.Sö, kmen
Chin. Phys. Lett. 2004, 21 (12): 2500-2503 .  
Abstract   PDF(pc) (375KB) ( 364 )
We have calculated variationally the ground state binding energy of a hydrogenic donor impurity in a parabolic quantum well in the presence of crossed electric and magnetic fields. These homogeneous crossed fields are such that the magnetic field is parallel to the heterostructure layers and the electric field is applied perpendicular to the magnetic field. The dependence of the donor impurity binding energy to the well width and the strength of the electric and magnetic fields are discussed. We hope that the obtained results will provide important improvements in device applications, especially for a suitable choice of both fields in the narrow well widths.

esonant Optical Absorption in Semiconductor Quantum Wells
YU Li-Yuan, CAO Jun-Cheng
Chin. Phys. Lett. 2004, 21 (12): 2504-2506 .  
Abstract   PDF(pc) (334KB) ( 405 )
We have calculated the intraband photon absorption coefficients of hot two-dimensional electrons interacting with polar-optical phonon modes in quantum wells. The dependence of the photon absorption coefficients on the photon wavelength λ is obtained both by using the quantum mechanical theory and by the balance-equation theory. It is found that the photon absorption spectrum displays a local resonant maximum, corresponding to LO energy, and the absorption peak vanishes with increasing the electronic temperature.

Mechanisms and Concentration Dependence of Upconversion Fluorescence in Er3+ and Tm3+ Codoped Tellurite Glasses
SHEN Xiang, NIE Qiu-Hua, XU Tie-Feng, PENG Tao, GAO Yuan
Chin. Phys. Lett. 2004, 21 (12): 2507-2510 .  
Abstract   PDF(pc) (510KB) ( 448 )
We investigate the upconversion luminescence of Er3+ and Tm3+ codoped tellurite glasses under both the 975 and 800nm excitations. By Tm3+ codoping, the Er3+ green emission corresponding to the (4S3/2, 2H11/2) → 4I15/2 transitions was quenched, while the red emission corresponding to the 4 F9/24I15/2 transition was selectively sensitized. The red emission has a maximum in the range where the ratio of Er3+- to Tm3+-content is about two and its fluorescence intensity becomes 1.5 and 5 times larger at the maximum than those in the absence of Tm3+ for 975 and 800nm excitations, respectively. The results were explained considering the influence of energy transfers between these two active ions.


Enhancement of Critical Current Density in Graphite Doped MgB2 Wires
XU Hong-Liang, , FENG Yong, XU Zheng, YAN Guo, CAO Lie-Zhao, LI Xiao-Guang
Chin. Phys. Lett. 2004, 21 (12): 2511-2513 .  
Abstract   PDF(pc) (369KB) ( 514 )
Graphite doped MgB2-xCx (x = 0.00, 0.05, 0.10) wires were fabricated via the in situ powder-in-tube method in flowing argon by using low carbon steel tubes as the sheath materials. With the increase of graphite concentration, the amount of unreacted graphite in the core area increases, and the average grain size of MgB2 decreases. It is found that the critical current density Jc can be significantly improved by graphite doping. The MgB2 wire with x = 0.05 exhibits the best Jc value of 16710A/cm2 at 6K, 4.5T, but the MgB1.9C0.1 wire has the highest Jc value of 2060 A/cm2 at 6K, 8T. It is suggested that the enhancement of Jc is due to not only the improvement of the microstructure features but also the introduction of pinning centres.
Superconducting Transition Temperature and Metal--Semiconductor Transition Temperature in YBa2Cu4O8/La0.67Ca0.33MnO3/YBa2Cu4O8 Trilayer Films
ZHAO Kun, HUANG Yan-Hong, FENG Jia-Feng, WONG Hong-Kuen
Chin. Phys. Lett. 2004, 21 (12): 2514-2517 .  
Abstract   PDF(pc) (344KB) ( 384 )
YBa2Cu4O8/La0.67Ca0.33MnO3/YBa2Cu4O8(YBCO/LCMO/YBCO) trilayer films were prepared by magnetron facing-target sputtering. For the first time, the oscillatory behaviour of superconducting transition temperature Tc,ON with the thickness of LCMO (dL) has been observed. The strongest nonmonotonic information in the Tc,ON--dL curves appears clearly when dL is larger than the critical thickness dLCR. The metal--semiconductor transition temperature can only be detected at dL>dLCR. The dependence on the ferromagnetic spacer layer in YBCO/LCMO/YBCO systems suggests strongly the interplay of ferromagnetic and superconducting couplings.
Measurements of Absorption and Anisotropy Coefficients of the Fat Emulsion Intralipid-10%
ZHANG Lian-Shun, ZHANG Lin, ZHANG Chun-Ping, QI Sheng-Wen, XU Tang, TIAN Jian-Guo
Chin. Phys. Lett. 2004, 21 (12): 2517-2520 .  
Abstract   PDF(pc) (300KB) ( 1001 )
We report measurements of absorption and anisotropy coefficients of the fat emulsion Intralipid-10%. Anadding-absorber method is used for measurement of absorption and anisotropy coefficients of the Intralipid-10%. Using the diffusion theory which has been extended to include anisotropy scattering for a point-source in infinite-medium geometry, we found that the standard deviations of multiple measurements for √μa/D are less than 0.6% and the residuals between the measured data and the fits have rms values of 0.1%, where μa is the absorbing coefficient of the solution in our experiment and D is the diffusion coefficient of the medium. The values of the standard deviations and the residuals demonstrate the high precision of the measurements.
Ultrafast Energy Transfer and Enhanced Two-Photon Absorption in a Novel Porphyrin Side-Chain Polymer
WANG Hui, HUANG Ya-Ping, DENG Li, ZHAO Fu-Li, LIN Wei-Zhu, WANG Jian, LIANG Zhao-Xi
Chin. Phys. Lett. 2004, 21 (12): 2521-2524 .  
Abstract   PDF(pc) (541KB) ( 409 )
Ultrafast relaxation processes and transient two-photon absorption are studied in a novel porphyrin side-chain polymer, 5-hydroxy-10,15,20-triphenyl-porphyrin-poly(glycidyl methacrylate) (HTPP-PGMA), by using picosecond luminescence spectroscopy and femtosecond pump--probe techniques. HTPP-PGMA exhibits the ultrafast initial luminescence decay (~300ps), which is absent in the conventional porphyrin monomer such as TPP. Enhanced two-photon absorption was observed in HTPP-PGMA; the corresponding Im x(3) is about 2.8× 1011esu, which is almost one order of magnitude larger than that of the conventional porphyrin monomer (TPP) (~1.3×1012esu). The ultrafast energy transfer plays an important role in the excited-state relaxation dynamics observed in HTPP-PGMA. The potential application of HTPP-PGMA in optical switching is discussed.
Excited-State Dynamics of a Novel Bisimide--C60 Complex
FU Li-Min, XIAO Sheng-Qiang, AI Xi-Cheng, ZHANG Jian-Ping, ZOU Bing-Suo, LI Yu-Liang, NIE Yu-Xin
Chin. Phys. Lett. 2004, 21 (12): 2525-2528 .  
Abstract   PDF(pc) (484KB) ( 485 )
The excited-state dynamics of a bisimide derivative (Z1) and a novel Z1--C60 complex (PSF) has been investigated by means of steady state optical spectroscopies and femtosecond time-resolved absorption spectroscopies. The lifetime of the singlet excited state of Z1 shortens drastically from 2.4ns to 1.7ps upon going from Z1 to PSF, a significant kinetics change is in coincidence with the complete fluorescence quench caused by the C60 attachment. Highly efficient Z1-to-C60 excitation energy transfer which is governed by the mechanism of Z1--C60 electron exchange has been verified for the PSF complex.
Abnormal Energy Dependence of Photoluminescence Decay Time in InGaN Epilayer
HUANG Jin-Song, LUO Xiang-Dong, YANG Xu-Dong, SUN Zheng, SUN Bao-Quan, XU Zhong-Ying, GE Wei-Kun
Chin. Phys. Lett. 2004, 21 (12): 2529-2532 .  
Abstract   PDF(pc) (461KB) ( 616 )
We employ photoluminescence (PL) and time-resolved PL to study exciton localization effect in InGaN epilayers. By measuring the exciton decay time as a function of the monitored emission energy at different temperatures, we have found unusual behaviour of the energy dependence in the PL decay process. At low temperature, the measured PL decay time increases with the emission energy. It decreases with the emission energy at 200K, and remains nearly constant at the intermediate temperature of 120K. We have studied the dot size effect on the radiative recombination time by calculating the temperature dependence of the exciton recombination lifetime in quantum dots, and have found that the observed behaviour can be well correlated to the exciton localization in quantum dots. This suggestion is further supported by steady state PL results
Photoluminescence Characterization of Silicon Nanoparticles Hybridized Europium Complex
RAN Guang-Zhao, BIAN Zu-Qiang, LIU Shi-Feng, HUANG Chun-Hui, QIN Guo-Gang,
Chin. Phys. Lett. 2004, 21 (12): 2533-2535 .  
Abstract   PDF(pc) (343KB) ( 563 )
A europium complex Eu (DBM)3 TPPO (Eu tris(benzoylmethide)- (triphenylphosphine oxide)) and silicon nanoparticles have been hybridized. The hybridization can evidently change the photoluminescence (PL) characteristics of the Eu complex in the following aspects: under an excitation of 390nm, the intensity of the PL peak at 611nm due to the 5D0--7F2 transition of the Eu3+ ions has been increased by 30%, and the integrated PL intensity in the visible range has been increased by nearly 3 times; the PL excitation efficiency beyond 440nm has been improved evidently; the peak in the PL excitation spectrum shifts from 408 to 388nm, and the PL decay time decreases from 2.07 to 0.96μs. The experimental results indicate that in the PL process, the photoexcited energy may transfer from the silicon nanoparticles to the Eu3+ ions.
Optical Absorption Spectra and Intraband Dynamics in Terahertz-Driven Semiconductor Superlattice
MI Xian-Wu
Chin. Phys. Lett. 2004, 21 (12): 2536-2539 .  
Abstract   PDF(pc) (532KB) ( 674 )
We have theoretically investigated the optical absorption spectrum and intraband dynamics by subjecting a superlattice to both a terahertz (THz)-frequency driving field and an optical pulse by using an excitonic basis. In the presence of a THz dc field, the satellite structures in the absorption spectra are presented. The satellite structure is a result from the THz nonlinear dynamics of Wannier--Stark ladder excitons. On the other hand, the coherent intraband polarization is investigated. We find that the excitonic Bloch oscillation is driven by the THz field and yields an intraband polarization that continues to oscillate at times much longer than the intraband dephasing time. The temporal evolution of the slowly varying components of the intraband polarization is dependent on the THz frequency.
Single Crystal Si Layers on Glass Fabricated by Hydrophilic Fusion Bonding and Smart-Cut Technology
ZHEN Wan-Bao., LIU Wei-Li, SONG Zhi-Tang, FENG Song-Lin, ZHU Shi-Fu, ZHAO Bei-Jun
Chin. Phys. Lett. 2004, 21 (12): 2540-2542 .  
Abstract   PDF(pc) (263KB) ( 693 )
A single crystal Si thin film on a glass substrate has been obtained successfully by hydrophilic fusion bonding and the smart-cut technology. Tensile strength testing shows that the bonded interface has strong adhesion and the bonding strength is about 8.7MPa. Crystallinity and microstructure of the samples have been characterized by transmission electron microscopy (TEM). Electrical properties have also been investigated by Hall measurements and four-point probe. The mobility of the transferred Si layer on glass is about 122cm2/V.s. The results show that the single-crystal silicon layer transferred onto glass by direct bonding keeps good quality for the applications of integrated circuits, transducers, and flat panel display.
Mechanical Properties of Breast Cancer Cell Membrane Studied with Optical Tweezers
GUO Hong-Lian, LIU Chun-Xiang, DUAN Jian-Fa, Jiang Yu-Qiang, HAN Xue-Hai, LI Zhao-Lin, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2004, 21 (12): 2543-2546 .  
Abstract   PDF(pc) (590KB) ( 819 )
Membrane tethers are extracted from breast cancer cells using a force generated by an optical trap. It is experimentally obtained that the radius of tether is about 0.1μm and the static tether force is about
8.5 pN. Calculations based on the experimental measurements give a bending modulus for the tether of 1.35×10-19Nm and a surface membrane tension of 6.76×10-6N/m in the breast cancer
cell. The treatment with cytochalasin D results in the decreasing bending modulus and decreasing apparent surface tension. When the membrane protein caveolin is over-expressed, similar cases occur in bending modulus and apparent surface tension. In addition, the viscous resistance coefficient of the membrane is calculated to be 1.15pN.s/μm according to the dynamic tether forces obtained under different pulling velocities.
A Multiple Scattering Theory for Proton Penetration
YANG Dai-Lun, WU Zhang-Wen, JIANG Steve-Bin, LUO Zheng-Ming
Chin. Phys. Lett. 2004, 21 (12): 2547-2550 .  
Abstract   PDF(pc) (406KB) ( 483 )
We extend the electron small-angle multiple scattering theory to proton penetration. After introducing the concept of narrow energy spectra, the proton energy loss process is included in the proton deep penetration theory. It precisely describes the whole process of proton penetration. Compared to the Monte Carlo method, this method maintains the comparable precision and possesses much higher computational efficiency. Thus, it shows the real feasibility of applying this algorithm to proton clinical radiation therapy.
Standing Rankine--Hugoniot Shocks in Black Hole Accretion Discs
GU Wei-Min, LU Ju-Fu
Chin. Phys. Lett. 2004, 21 (12): 2551-2554 .  
Abstract   PDF(pc) (340KB) ( 474 )
We study the problem of standing shocks in viscous disc-like accretion flows around black holes. For the first time we parametrize such a flow with two physical constants, namely the specific angular momentum accreted by the black hole j and the energy quantity K. By providing the global dependence of shock formation in the j-K parameter space, we show that a significant parameter region can ensure solutions with Rankine--Hugoniot shocks; and that the possibilities of shock formation are the largest for inviscid flows, decreasing with increasing viscosity, and ceasing to exist for a strong enough viscosity. Our results support the view that the standing shock is an essential ingredient in black hole accretion discs and is a general phenomenon in astrophysics, and that there should be a continuous change from the properties of inviscid flows to those of viscous ones.

Geographical Effects on Complex Networks
LIN Zhong-Cai, YANG Lei, YANG Kong-Qing,
Chin. Phys. Lett. 2004, 21 (12): 3214-3217 .  
Abstract   PDF(pc) (232KB) ( 462 )
We investigate how the geographical structure of a complex network affects its network topology, synchronization and the average spatial length of edges. The geographical structure means that the connecting probability of two nodes is related to the spatial distance of the two nodes. Our simulation results show that the geographical structure changes the network topology. The synchronization tendency is enhanced and the average spatial length of edges is enlarged when the node can randomly connect to the further one. Analytic results support our understanding of the phenomena.
65 articles